The invention relates to a method of feeding a clutch cylinder of a hydraulically actuated clutch system.
From the EP 1 767 824 A1 a hydraulically actuated clutch system as a part of a dual clutch transmission in a motor vehicle is known comprising a first clutch and a second clutch. Both clutches are assigned to one clutch cylinder each, allowing to close the clutch against a force from a clutch release spring. The required pressure for closing the clutch is provided by a hydraulic system providing via a pump via a main pressure control a system pressure. Each clutch of the dual clutch transmission is in addition assigned to the system pressure at the valve inlet and to a clutch pressure at a valve outlet for actuating the clutch. The clutch is connected to the clutch cylinder.
From the prior art it is known for creating a short filling time and therefore a shorter switching time in a dual clutch transmission to close the clutch cylinder in a clutch starting from the open position to an engagement point to provide a particular filling pressure over a certain time period that is significantly higher than the engagement point pressure that is necessary for maintaining the clutch at its engagement point. The engagement point of the clutch is that position of the clutch where the clutch linings abut against each other, but the force pressing the clutch linings against each other is zero or so low that practically no torque transmitting capacity is established. After terminating the filling pressure the engagement point pressure is then applied as a target pressure.
For creating a short filling time, a high value for the filling pressure can be set over a short period of time. However, this creates the risk that after terminating the filling pressure, the pressure in the clutch cylinder may exceed, due to dynamic effects, the engagement point pressure and therefore close the clutch beyond its engagement point, establishing an undesired torque transmitting capacity. This may result in a noticeable impact that is perceived as disadvantageous for the driving comfort. Providing a method for fast filling without affecting the driving comfort is difficult.